1. Field of the Invention
This invention relates to a mounting head for use in an electronic component-mounting apparatus for picking up electronic components by vacuum and mounting the electronic components on a circuit board.
2. Prior Art
Conventionally, a mounting head for an electronic component-mounting apparatus of this kind has been proposed by Japanese Laid-Open Patent Publication (Kokai) No. 5-226884, which includes a nozzle holder having a plurality of suction nozzles mounted thereon in a manner capable of projecting and retracting vertically, and a holder support member secured to a bracket mounted on a body of the electronic component-mounting apparatus, for rotatably supporting the nozzle holder via a pair of upper and lower bearings. The nozzle holder has a hook support member mounted at an upper portion thereof. The hook support member has a plurality of engaging hooks corresponding to the suction nozzles, respectively, and extending perpendicularly downward from the hook support member in a pivotally movable manner. Further, the hook support member has an upper end surface thereof formed with engaging grooves for engagement with an output end of a rotation drive mechanism arranged in the apparatus body. That is, the output end of the rotation drive mechanism engages with the engaging groove to drive the nozzle holder for rotation, whereby one of the suction nozzles selected for use is brought to a projecting position.
Each of the suction nozzles has a hook-catching member fixed to an upper portion thereof for engagement with a corresponding one of the engaging hooks. Retraction of the suction nozzles into the nozzle holder is effected by lowering the mounting head and causing the suction nozzles to strike against a nozzle stopper, while downward projection of a selected suction nozzle from the nozzle holder is effected by pivotally moving a corresponding one of the engaging hooks by a disengaging mechanism provided in the apparatus body, to disengage the engaging hook from a corresponding one of the hook-catching members. That is, in changing (switching) suction nozzles in use, the nozzle holder is rotated to bring a suction nozzle selected for use in a next mounting operation to a projecting position, then all the suction nozzles are struck against the stopper to be once retracted into the nozzle holder, and thereafter, only the selected suction nozzle is caused to project.
As described above, in the conventional mounting head, all the suction nozzles are required to be struck against the stopper before causing one of the suction nozzles to project for use. Since this operation is repeatedly carried out, the striking end of each suction nozzle is worn away or deformed, which inevitably shortens the service life of the suction nozzle. Further, it is required to bring the suction nozzles to the location of the nozzle stopper to carry out the retracting operation before causing the projection of the selected suction nozzle, and hence it takes a considerable time to cause the selected suction nozzle to project. This is a significant factor causing an increase in tact time of an overall operation for mounting electronic components on a circuit board.